Method for producing poly-(1,4-phenylenazine-N,N-dioxide) by oxidizing p-benzoquinonedoxime

ABSTRACT

The invention relates to a method for producing poly(1,4-phenylenazine-N,N-dioxide) and derivatives thereof which are substituted in the ring, by oxidizing p-benzoquinonedioxime or the corresponding derivative thereof which is substituted in the ring, using polyanions of the halogens bromine or iodine. Tribromide Br3- or triiodide I3- can be used as polyanions and these can be obtained in situ from H2O2 and a bromide or iodide.

DESCRIPTION

The invention relates to a process for preparingpoly-(1,4-phenyleneazine-N,N-dioxide), which is also calledpoly-N,N-diazadioxide, and its nuclearly-substituted derivatives byoxidation of p-benzoquinonedioxime or its correspondingnuclearly-substituted derivatives, by means of polyanions of thehalogens bromine or iodine.

Poly-(1,4-phenyleneazine-N,N-dioxide) is a highly effective cross-linkerin rubber mixtures or rubber/metal binding agents. Moreover, the use ofthis substance as a reusable evaporation chemical for the manufacture ofelectronic circuits by way of laser inscriptions (SolventlessLaser-Imageable Resist Process) is also known.

Principally available for the synthesis ofpoly-(1,4-phenyleneazine-N,N-dioxide) is only an oxidative path,starting from p-benzoquinonedioxime or its nuclearly-substitutedderivatives, because the reduction of the corresponding nitro compoundscannot be kept at the level of the nitroso compound. Chlorine, nitrogenmonoxide/sodium hypochlorite, sodium chlorate, nitric acid, iron IIIchloride and potassium hexacyanoferrate (III), for example, are known asoxidising agents.

The primary reaction product of all of the above-mentioned oxidationreactions is a dinitroso compound. A characteristic of almost allp-dinitroso compounds is their spontaneous polymerisation to formpoly-N,N-azodioxides. For example, p-dinitrosobenzene is present as amonomer at −240° C. and as a dimer or oligomer between −90° C. and −50°C. At higher temperatures (−10° C. to 100° C.), onlypoly-(1,4-phenyleneazine-N,N-dioxide) is still found.

A disadvantage to some extent of the manufacturing processes knownhitherto is, in most cases, the enormous salt load which accumulates.The following table gives examples of this:

TABLE 1 Salt load produced in the oxidation of p- benzoquinonedioxime asa function of the oxidising agent used. Salt load per 100 kg Oxidisingagent poly-N,N-azodioxide K₃[Fe(CN)₆] 510 kg complex salt FeCl₃ 184 kgFeCl₂ NO/NaOCl 85 kg NaCl NaClO₃/HCl 85 kg NaCl

Other processes are salt-load-free, but have other disadvantagesinstead. Thus, oxidation by means of nitric acid with yields of <80% isless economical and, because of the necessity of having to wash thereaction product effectively, a disadvantageous formation of waste waterresults.

Oxidation with elemental chlorine first of all takes place in asalt-load-free manner by forming hydrochloric acid, as does oxidation inthe H₂O₂/hydrochloric acid system. In this case, elemental chlorine isreleased in situ from hydrochloric acid and hydrogen peroxide (equation1). Chlorine is also used in this case as the actual oxidising agent.

 2 HCl+H₂O₂→Cl₂+2 H₂O  (1)

Cl₂+H₂O₂→2Cl⁻+2 H⁺+O₂  (2)

The possible reaction of the chlorine which is formed with hydrogenperoxide in accordance with equation (2) can lead to the release ofoxygen. Direct oxidation of p-benzoquinonedioximes with hydrogenperoxide is not observed, even in the case of a raised reactiontemperature.

In this process, the mother liquor which results, including any washwater which may be required, has to be neutralised, which in turn leadsto the creation of a salt load. It is also disadvantageous thatcontinuing oxidation of the reaction product to form p-dinitrosocompounds cannot be ruled out. These compounds are explosive and highlytoxic.

In the context of mechanistic considerations, A. Ermakov and Y. F.Komkova (Zh. Org. Khim. 20, 10, 2252 (1984)) refer, corresponding to theoxidation with chlorine (from H₂O₂/hydrochloric acid), to the oxidationwith iodine formed in situ (from H₂O₂ and potassium iodide) analogouslyto equation (1). A manufacturing process with iodine or iodine formed insitu is not described in this text, however.

The direct conversion of p-benzoquinonedioxime with elemental iodine(Comparative Example A) leads, however, to the primary dinitroso productonly after relatively long reaction times in a reaction which is notvery uniform, and the product can moreover be obtained only in very lowyields. Elemental iodine thus appears to be an oxidising agent which isnot very suitable for the industrial oxidation ofp-benzoquinonedioximes.

Thus, until now, there has not been an industrial process which allowsthe quantitative oxidation of p-benzoquinonedioximes to form thecorresponding poly-N,N-diazadioxides with strict avoidance of theformation of toxic dinitro by-products, and which additionally avoids asalt load, even an indirect one.

The object of the invention is therefore to overcome the disadvantagesof the prior art and to develop a process for preparingpoly-(1,4-phenyleneazine-N,N-dioxide) and its nuclearly-substitutedderivatives, which process is distinguished by a complete conversion ofthe reaction partners whilst excluding the formation of dinitroderivatives, the avoidance of salt loads and a clear reduction in theamounts of waste water.

The object is achieved by the process presented in claim 1. Claims 2 to12 develop the process further.

Surprisingly, it has been found that easily accessible derivatives ofthe halogens, namely the polyanions, lead to a clear increase in thechemical selectivity of the oxidation reactions described above.Polyanions (X_(Z) ⁻, z ≧3) of the halogens (X) are very easilyaccessible by means of the conversion of halide ions (X⁻) with theelements, for example:

X₂+X⁻→X₃ ⁻  (3)

With increasing atomic number, trihalides of chlorine, bromine andiodine form increasingly easily, as is evident from the equilibriumconstants in accordance with Table 2 that apply for the solvent water.

Table 2: Equilibrium constants of the trihalide formation in water(X₂+X⁻→X₃ ⁻)

K_(chlorine)=0.01

K_(bromine)=18

K_(iodine)=725

It can be seen that a very large excess of chloride ions is required inorder to form trichloride ions (Cl₃ ⁻). Experiments with risingconcentrations of chloride ions in the HCl/H₂O₂ system actually lead toan increased chemical selectivity of the oxidation process.

If the oxidation is carried out at a given temperature in 15%hydrochloric acid, the poly-N,N-diazadioxide is obtained with yields of90 to 95% and contains approximately 1% p-dinitrobenzene. An increase inthe concentration of hydrochloric acid to 25 or 35% leads, withdinitrobenzene contents of only 6000 or 1200 ppm, respectively, in theend product, to a clear reduction in the formation of by-products. Theincreased chemical selectivity, however, is linked with a reduction inthe isolated yields to approximately 80%. Therefore, the alteration ofthe redox potentials that accompanies the variation of the chloride ionconcentration thereby leads to a loss of reactivity.

Because of the comparatively great equilibrium constants (Table 2) inthe case of the halogens bromine and iodine, the bromide concentrationor iodide concentration does not have to be chosen to be as high inorder to obtain a comparatively great selectivity. Therefore, only thepolyanions of the bromine and of the iodine are of practicalsignificance for the process in accordance with the invention, in whichcase mainly tribromide or triiodide are used. The oxidising polyanionsare to be used in at least a stoichiometric amount and at most in doublethe stoichiometric amount.

Advantageously, the corresponding alkali compound can be used as thetribromide or triiodide.

Instead of being added separately, the tribromide or triiodide can alsobe produced in situ from a bromide compound or iodide compoundrespectively and H₂O₂, in which case the corresponding alkali compoundis advantageously used.

Particularly advantageously, the process can be carried out if triiodide(I₃ ⁻) is selected as the oxidising agent, which is obtained in situfrom an alkali iodide and H₂O₂. The alkali iodide can thereby be used ina catalytic to stoichiometric amount of 0.1 to 100% by mol, with respectto the amount of p-benzoquinonedioxime. In accordance with theequilibrium constants listed in Table 2, the iodide which is primarilyformed reacts spontaneously to form alkali triiodide. A violet colouringby elemental iodide is therefore not observed. The reaction of thetriiodide obtained in this way with p-benzoquinonedioxime leadsselectively to the formation of poly-N,N-diazadioxides and iodide ions.

As a result of a controlled addition of further hydrogen peroxide,triiodide is formed anew from the iodide which is released. A catalysiscycle results, and LiI, NaI, KI, RbI or CsI can also be used in smallamounts, i.e. not stoichiometric dosages, for the synthesis. A preferredcharge amount of the alkali iodide is 1 to 5% by mol, with respect tothe amount of p-benzoquinonedioxime used.

The H₂O₂ amount that is added typically amounts to 100 to 110% by mol,with respect to p-benzoquinonedioxime.

A preferred process variant is typically carried out as follows:p-benzoquinonedioxime (or one of its nuclearly-substituted derivatives)is suspended in water and mixed with 1 to 5% by mol of an alkali iodide.The well-stirred suspension is then mixed with 100 to 110% by mol H₂O₂(with respect to p-benzoquinonedioxime used) in the form of a 30%hydrogen-peroxide solution at a temperature of between 10 and 65° C. for2 to 4 hours. After the addition has ended, stirring is continued at thegiven temperature for another 1 to 2 hours in order to complete thereaction. The yellow to light-brown reaction product is filtered andwashed with a little water. The mother liquor and filtrate are cleanedand can be used again without further treatment for the synthesis, sothat ideally no waste water results.

Preferably, the process in accordance with the invention is carried outat a pH value of approximately 3 to 7. At this pH value, the processproduct poly-(1,4-phenyleneazine-N,N-dioxide), or one of itsnuclearly-substituted derivatives, is formed in very good yields as aneasily filterable, crystalline deposit. A lower pH value tends to leadto poorer yields, a higher pH value has the result that the productprecipitates as a poorly filterable, amorphous mass. Corrections to thepH value can, for example, be carried out with small amounts of alkalihydroxide, such as NaOH or KOH, or, for example, with small amounts ofmineral acids, such as HBr or HI.

The poly-(1,4-phenyleneazine-N,N-dioxide) prepared according to theprocess in accordance with the invention is free of p-dinitrobenzene.Even a 100% excess of H₂O₂ does not lead to a formation of dinitroderivatives. The process is thus highly chemically selective.

The isolated yields in the preferred triiodide oxidation process thuslie between 96 and 100%, which corresponds to a quantitative conversion.

The subject-matter of the invention is explained in greater detail withthe aid of the following examples:

Comparative Example A: Oxidation of p-benzoquinonedioxime with elementaliodine (I₂)

27.6 g of p-benzoquinonedioxime (CD) (0.20 mol) and 25.4 g of iodine(0.10 mol) in 320 ml water were stirred in a round-bottom flask at roomtemperature. After 2 days, a sample was taken and dried. The solid whichwas obtained was almost completely soluble in chloroform. The formationof poly-(1,4-phenyleneazine-N,N-dioxide), which is not very soluble inchloroform, could therefore be ruled out to a great extent. After areaction time of a further 6 days, the reaction mixture was concentratedby evaporation in order to dry it and then absorbed in chloroform. Afterfiltration and drying, only 0.90 g of a brown-black solid could beisolated. In addition to other products, the IR spectrum indicates thepresence of poly-(1,4-phenyleneazine-N,N-dioxide).

Examples 1 to 9: Oxidation of p-benzoquinonedioxime with triiodide I₃ ⁻

In Examples 1 to 9, the following general procedure was followed:

41.4 g of p-benzoquinonedioxime (CD) (0.30 mol) in 250 ml water wasplaced in a 1 l four-necked flask with KPG stirrer, drip funnel, refluxcondenser and internal thermometer and mixed with an appropriate amountof alkali iodide (see Table 3). Then, 35.5 g of Perhydrol (H₂O₂ 30%)(0.31 mol H₂O₂) was added to this mixture dropwise over 3 hours, in sucha way that the internal temperature of the reaction vessel wasconstantly between 20 and 40° C. Depending on the purity of the startingsubstances, the pH value was between 2.6 and 5.5.

After this, stirring was continued for 1 hour, the mixture was thenfiltered and washed with 50 ml water. The yellow-brown solid which wasobtained was then dried in the desiccator over P₂O₅ until constantweight and identified by means an of IR spectrum. The yields of thepoly-(1,4-phenyleneazine-N,N-dioxide) obtained in each case are listedin Table 3.

TABLE 3 Alkali iodide and its charge amount, and also yields of thepoly-(1,4-phenyleneazine-N,N-dioxide) obtained charge amount of alkalialkali iodide yield Example iodide [g]/[mol %] on CD [g]/[%] 1 NaI2.25/5.00 40.7/99.7 2 KI 0.50/1.00 38.7/94.8 3 KI 1.25/2.50 39.8/97.5 4KI 2.50/5.00 39.7/97.2 5 CsI 1.95/2.50 39.8/97.5 6 CsI 3.90/5.0039.9/97.8 7 KI + CsI* 1.25 1.95/2.50 2.50 39.8/97.5 8 CsI** 3.90/5.0039.8/97.5 9 CsI*** 3.90/5.00 40.6/99.5 *The reaction was carried out at40-50° C. and heated to 65° C. for the after-reaction. **Mother liquorfrom example 6. ***H₂O₂ was added with 100% excess; after-reaction 2hours.

In all cases, the IR spectrum displayed chemical identity with areference spectrum. P-dinitrobenzene could not be detected in any case(GC, chloroform extract against external standard). The products wereall very easily filterable. Under the raster electron microscope, theydisplayed pellet-shaped and rod-shaped crystals with an edge length of0.5 to 5 μm (sporadically up to 40 μm), which generally settled togetherto form spherical agglomerates of 10 to 20 μm.

What is claimed is:
 1. A process for preparingpoly-(1,4-phenylenazine-N,N-dioxide) and its nuclearly-substitutedderivatives comprising oxidizing p-benzoquinonedioxime or itscorresponding nuclearly-substituted derivatives with polyanions of thehalogens bromine or iodine.
 2. The process according to claim 1, whereinsaid polyanion is selected from the group consisting of tribromide andtriiodide.
 3. The process according to claim 2, wherein said tribromideis at least one alkali tribromide selected from the group consisting ofLiBr₃, NaBr₃, KBr₃, RbBr₃ and CsBr₃.
 4. The process according to claim2, wherein said tribromide is obtained in situ from the correspondingbromide Br⁻ and hydrogen peroxide H₂O₂.
 5. The process according toclaim 2, wherein said triiodide is an alkali triiodide selected from thegroup consisting of LiI₃, NaI₃, KI₃, RbI₃ and CsI₃.
 6. The processaccording to claim 2, wherein said triiodide is obtained in situ fromthe corresponding iodide I⁻ and hydrogen peroxide H₂O₂.
 7. The processaccording to claim 5, wherein said alkali iodide is present in an amountof from 0.1 to 100% by mol relative to the p-benzoquinonedioxime or toone of its nuclearly-substituted derivatives.
 8. The process accordingto claim 6, wherein said alkali iodide is present in an amount of from0.1 to 100% by mol relative to the p-benzoquinonedioxime or to one ofits nuclearly-substituted derivatives.
 9. Process according to claim 7,wherein the alkali iodide is present in an amount of from 1 to 5% by molrelative to the p-benzoquinonedioxime or to one of itsnuclearly-substituted derivatives.
 10. Process according to claim 8,wherein the alkali iodide is present in an amount of from 1 to 5% by molrelative to the p-benzoquinonedioxime or to one of itsnuclearly-substituted derivatives.
 11. The process according to claim 6,wherein the H₂O₂ is used in an amount of 100 to 110% by mol relative tothe p-benzoquinonedioxime or to one of its nuclearly-substitutedderivatives.
 12. The process according to claim 1, wherein saidp-benzoquinonedioxime or one of its nuclearly-substituted derivatives issuspended in water before the oxidation.
 13. Process according to claim1, wherein the reaction temperature is 10 to 65° C.
 14. Processaccording to claim 1, wherein the reaction is carried out at a pH offrom 3 to 7.